Very large scale systems that provide services, such as Internet search systems and instant communications systems, are treated differently from conventional enterprise networking systems. For example, such very large scale systems are not only designed for a much larger scale, but have distinct characteristics, and are operated with specialized tools.
As enterprise IT environments evolve and move towards models in which software is a service, many common business applications need to be built in very large-scale versions. Further, many enterprises are deploying very large scale systems that have characteristics and service level requirements similar to those common in Internet services.
However, the tools currently used in enterprise IT environments are ill-suited for such large scale systems. Partly as a result, building a highly available, truly large-scale application today is more of an art than a science, whereby only a relatively small, elite number of designers with rare, specialized skills know how to build these types of systems. The scarcity of such designers and resultant expense are one reason that such large scale systems are not in the mainstream.